1. Field of the Invention
This invention relates to biological methods and products useful in agriculture. More specifically, the present invention is directed to a novel turkey astrovirus, nucleic acid encoding the novel turkey astrovirus, primers sequences to the novel turkey astrovirus, methods for detecting avian astroviruses, and vaccines to avian astroviruses.
2. Description of the Related Art
Astroviruses are small nonenveloped, positive sense RNA viruses, which are distinct among the other closely related small round, positive stranded RNA viruses such as calciviruses and picornaviruses (Carter, Arch. Virol. Suppl., Volume 9, 429-439, 1994; Monroe et al., J. Virol., Volume 67, 3611-3614, 1993; Willcocks et al., J. Gen. Virol., Volume 75, 1785-1788, 1994). Astroviruses cause enteric disease in the young of several species including mammals and poultry (Aroonprasert et al., Vet. Microbiol., Volume 19, 113-125, 1989; Bridger et al., Infect. Immun., Volume 43, 133-138, 1984; Geyer et al., J. S. Afr. Vet. Assoc., Volume 65, 164-166, 1994; Gorbalenya et al., FEBS Lett., Volume 243, 103-114, 1989; Harbour et al., Vet. Rec., Volume 120, 555-557, 1987; Herring et al., J. Gen. Virol., Volume 53, 47-55, 1981; Hoshino et al., Arch. Virol., Volume 70, 373-376, 1981; Kjedlsberg et al., Arch. Virol., Volume 84, 135-140, 1985; Marshall et al., Aust. Vet. J., Volume 61, 33-38, 1984; Matsui et al, In: Fields Virology, third edition, Fields et al. (Eds.), Lippincott-Raven, Publishers, Philadelphia, Volume 1, 811-824, 1996; McNulty et al., Vet. Rec., Volume 106, 561, 1980; Reynolds et al., Avian Dis., Volume 30, 728-735, 1986; Shimizu et al., J. Clin. Microbiol., Volume 28, 201-206, 1990; Snodgrass et al., Arch. Virol., Volume 55, 287-291, 1977; Tzipor et al., Vet. Rec., Volume 108, 286, 1981; Williams, Arch. Virol., Volume 66, 215-226, 1980; Woode et al., J. Med. Microbiol., Volume 11, 441-452, 1978) as well as fatal hepatitis in ducklings (Gough et al., Vet. Rec., Volume 114, 279, 1984).
Astrovirus disease in humans is one of the major causes of diarrhea in infancy and childhood. Greater-than 70% of children in the United States develop astrovirus antibodies before the age of 5 (Cook et al, J. Med. Microbiol., Volume 42, 1-2, 1995). Eight human astrovirus serotypes have been identified, and these are the only viruses within the family wherein the genome has been completely sequenced (Matsui et al., 1996, supra; Monroe et al, U.S. Pat. No. 5,625,049, Apr. 29, 1997).
Astroviruses cause outbreaks of enteric disease in turkey poults. Astrovirus was first reported as a cause of gastroenteritis and mortality of turkeys 6 to 11 days of age in 1980 by McNulty et al (1980, supra). Since then there have been sporadic reports of astrovirus outbreaks in turkeys mostly related to enteritis and growth depression ( Reynolds et al., 1986, supra). Little is understood about astrovirus infection in turkeys, and detection has been dependent on EM and fluorescent antibody tests. However, this may be a function of the tools currently available for the diagnosis of astrovirus infections.
The human astrovirus has been described as approximately 6800 nucleotides (nt), and is organized into three open reading frames (ORF); 1a, 1b, and 2. From the 5xe2x80x2 end of the genome ORF 1a codes from the non-structural proteins identified as a serine protease, transmembrane helices, and a nuclear localization signal respectively (Cubitt, Arch. Virol. Suppl., Volume 12, 225-235, 1996). Next ORF 1b codes for the RNA dependent RNA polymerase (RDRP). ORFs 1a and 1b overlap by approximately 70 nt. ORF 1b is brought into frame by a retrovirus-like frameshift sequence that produces a stem loop (Marczinke et al., J. Virol., Volume 68, 5588-5595, 1994). At the 3xe2x80x2 end of the genome is ORF 2 which codes the capsid protein and is followed by an untranslated region and polyadenylated tail. ORF 2 is transcribed into a subgenomic message of approximately 2500 nt (Cubit, 1996, supra).
Detection of astrovirus in most species is limited to fluorescent antibody detection, and electron microscopy (EM). Both of these methods are time intensive and vulnerable to misdiagnosis. Fluorescent antibody tests may fail to recognize astrovirus antigens if the sample is infected with a different serotype (Matsui et al., 1996, supra). EM can also fail to detect the characteristic star-like surface projections, if the. sample is not processed correctly ( Caul et al., J. Med. Virol., Volume 9(4), 257-265, 1982). Furthermore, detection by cell culture is currently limited to bovine, feline, porcine, and human astroviruses (Harbour et al., 1987, supra; Lee et al., J. Gen., Virol., Volume 57 (2), 421-424, 1981; Shimuzu et al., 1990, supra; Woode et al., J. Clin. Microbiol., Volume 19 (5), 623-630, 1984).
While various astroviruses are known to cause enteric disease in several animal species including humans, there remains a need in the art for methods for detecting astrovirus in avians, especially poultry, which overcome some of the limitations of related art detection methods. The present invention described below is a novel turkey astrovirus, a novel nucleic acid encoding the turkey astrovirus, primers and probes for in-situ hybridization to avian astrovirus, methods for detecting the avian astrovirus using primers designed from the sequence of the novel turkey astrovirus, and vaccines to avian astroviruses. The present invention further describes antigenic polypeptides synthesized from the open reading frames 1a, 1b, and 2 of the novel turkey astrovirus nucleic acid.
It is, therefore, an object of the present invention to provide a novel turkey astrovirus for antigen production, vaccine production, antibody production, diagnostic primer or probe production, etc.
It is another object of the present invention to provide a turkey astrovirus nucleic acid sequence for production of antigenic polypeptides, vaccines, antibodies, primers, and probes for in-situ hybridization.
Another object of the present invention is to provide methods for detecting astrovirus in avians, especially poultry, more specifically turkeys, using antibodies, primers, or probes produced from a novel turkey astrovirus nucleic acid sequence.
A further object of the present invention is to provide a vaccine using a turkey astrovirus and/or a turkey astrovirus nucleic acid sequence.
Further objects and advantages of the present invention will become apparent from following description.